Manufacture of calcium hypochlorite

Abstract

A process for making calcium hypochlorite from caustic soda calcium hydroxide and chlorine by feeding to a stirred reactor an aqueous solution of the total required amount of caustic soda and an aqueous suspension of up to 80% by weight of the total required amount of calcium hydroxide, passing chlorine through the mixture until a redox potential of 650 to 800 mV is reached and while continuing chlorination adding the remaining of the calcium hydroxide at such rate with respect to chlorine that redox potential gradually increases to between 850 and 950 mV. This process prevents thickening and caking which are a recognized problem with conventional batch processes.

We claim: 
     
       1. A process for the preparation of calcium hypochlorite by interreaction of chlorine, sodium hydroxide and calcium hydroxide comprising the steps: (a) loading a stirred reactor with an aqueous solution of the total required amount of sodium hydroxide and from 10% to 80% by weight of the total required amount of calcium hydroxide as an aqueous suspension;   (b) passing chlorine through this suspension until the reaction mixture has reached a redox potential in the range of 650 to 800 mV;   (c) while continuing chlorination, continuously adding the remaining of the calcium hydroxide at such a rate with respect to chlorine that the redox potential gradually increases to a value from 850 to 950 mV; and   (d) collecting the resulting slurry of calcium hypochlorite; the temperature of the reaction mixture throughout the reaction being maintained in the range from 10° C. to 30° C.   
     
     
       2. A process as claimed in claim 1 wherein in Step (a) about 66% by weight of the total required amount of calcium hydroxide is fed to the reactor as an aqueous suspension. 
     
     
       3. A process as claimed in claim 1 wherein in Step (a) about 30% by weight of the total required amount of calcium hydroxide is fed to the reactor as an aqueous suspension. 
     
     
       4. A process as claimed in claim 1, 2 or 3 wherein in Step (c) the remaining of the calcium hydroxide is added in the form of an aqueous suspension. 
     
     
       5. A process as claimed in claim 1, 2 or 3 wherein the total amounts of the reagents added to the reactor are adjusted so that the molar ratio of calcium hydroxide to sodium hydroxide to chlorine is approximately 3:2:4.